1. Field of the Invention
The present invention relates to a grinding machine for grinding a frictional surface of a pad and also relates to a method of grinding the pad, in which a frictional surface of a substantially plate-shaped brake pad is ground so as to finish the brake pad to be a predetermined size and shape.
2. Description of the Related Art
Conventionally, a brake pad, for example, a brake pad used for a disk brake of an automobile is formed into a predetermined size and shape through the following processes. In a preforming process, base material, in which various granular and fibrous components are uniformly mixed, is compressed and formed into a predetermined size and shape with a preforming metallic mold. Subsequently, the preform is subjected to a heat forming process at a predetermined pressure and temperature using a heat forming metallic mold, so that it can be formed into a predetermined size and shape. Then, the heat formed object is cooled to a predetermined temperature. After cooling, the heat formed object is subjected to coating, grinding and chamfering if necessary.
FIGS. 10 and 11 are views showing the structure of a brake pad 1 that has completed the above cooling process.
The brake pad 1 includes: a frictional lining 2 and a back plate 3 fixed onto a reverse side of the friction lining 2. An overall shape of the brake pad 1 is substantially plain. In this brake pad 1, a surface of the friction lining 2 is a frictional surface 4 that is pressed against a brake disk so as to generate a brake force.
In this connection, components of the base material to compose the friction lining are: fibrous reinforcement composed of metallic fibers, inorganic fibers or organic fibers; a binder composed of thermosetting resin; and various additional agents such as a friction modifier or lubricant. In accordance with the physical property required for the friction lining, a compounding ratio of the components is appropriately adjusted.
The brake pad 1 shown in FIGS. 10 and 11 is subjected to grinding process in the finishing process conducted later, and as shown in FIGS. 12 and 13, when necessary, the frictional surface 4 is ground, both end portions 5 are chamfered, and the groove 6 used for radiation and drainage is formed. In this way, the brake pad 1 is finished to be a predetermined size and shape.
In this connection, an inclination angle, thickness t of the friction lining 2, provision or non-provision of the groove 6 and depth of the groove 6 are appropriately changed in accordance with the brake property required for a vehicle. According to the conventional method, grinding of the frictional surface, chamfering the end portions and grooving are respectively conducted in the different processes with different exclusive tools.
That is, both end portions 5 are chamfered in such a manner that several types of grinding tools (grinding wheels), the tool angles of which are different, are prepared in accordance with the number of inclination angles of chamfering, and that chamfering is conducted on the end portion with a predetermined tool. After that, in the process of grooving, the tool is replaced with a grooving cutter, so that the groove 6 is formed. After the formation of the groove 6 has been completed, the frictional surface 4 is ground with a tool for grinding a plane.
However, in the grinding process described above, the following problems may be encountered. When grooving is started after chamfering has been completed, or alternatively when grinding of frictional surface 4 is started after grooving has been completed, or when grinding of frictional surface is started after chamfering has been completed (in the case of non-provision of the groove), it is necessary to replace the tool every time. Moreover, even when the inclination angle of chamfering is changed, it is necessary to replace the tool. Since the tool must be frequently changed, the productivity is remarkably lowered. Therefore, it is impossible to apply the conventional grinding process to the system of small-lot production in which various types of products are produced.
In order to carry out grinding the frictional surface 4, chamfering and grooving, several passes of processing are required. In accordance with an increase in the number of grinding passes, productivity is greatly deteriorated.
Further, the number of types of tools to be prepared is increased, which increases the cost of tools. Furthermore, it takes time and labor to manage various types of tools. As a result, the manufacturing cost of pads is raised.